1. Field of the Invention
This invention pertains generally to biventricular implants, and more specifically to methods of operating those implants in order to manually, semi-automatically, or automatically optimize their operation.
2. Description of the Related Art
Deaths from cardiovascular diseases (“CVD”) is a very serious problem in the United States and throughout the world. Since 1900, CVD has been the No. 1 killer in the United States for every year (except for 1918).
The CDC estimates that each year around 400,000 people die of heart disease in an emergency department or before reaching a hospital; this accounts for a very large percentage of all cardiac deaths. A significant number of these deaths are not first events, but subsequent to first diagnosis and treatment of CVD. Consequently, there is much impetus to developing improved techniques for the care and management of CVD.
One such approach of recent vintage has been the integration of electrical and electronic devices into the care and management of CVD. As is evident in modern society, electronic devices have become ubiquitous. Everywhere we travel, we do so with the assistance and convenience afforded by these microminiaturized wonders. Watches, personal digital assistants, laptop computers, and cellular telephones are all recognizable and commonplace devices carried about by persons. However, as technology has permitted, these devices are not the only ones which may be carried with a person.
Many modern microelectronic devices are integrated or concealed within other devices or even within people. Pacemakers, hearing aids, automatic medication dispensers, bone growth stimulators, biological recorders and alarms, and even personal safety and alerting devices have become very prevalent within, on, or transported by people. It is extremely commonplace for many mechanical and even chemical devices to additionally include microelectronic devices, the electronics performing such diverse roles as timers, monitors, sensors, controls and a myriad of other functions. These functions may simply be more economical than a mechanical or chemical counterpart, but will often provide functions that would otherwise be impractical or impossible to achieve.
In recent years, substantial progress has been made in pacemakers and in the development of cardioverting and defibrillating techniques for effectively treating various heart disorders and arrhythmias. Past efforts have resulted in the development of implantable electronic pacemakers and standby cardioverters-defibrillators which, in response to the detection of an abnormal cardiac rhythm, discharge sufficient energy via electrodes connected to the heart to depolarize and restore it to normal cardiac rhythm. An early example of this cardioverting and defibrillating technique is disclosed in U.S. Pat. No. 3,942,536 of Mirowski et al, the teachings which are incorporated herein by reference. The Mirowski et al technique involves responses to a sensed peak right ventricular systolic pressure dropping below a fixed predetermined level and not returning above the predetermined level for a given period of time.
Efforts have also been directed toward developing techniques for reliably monitoring heart activity in order to determine whether cardioversion and defibrillation are desirable or necessary. Such techniques include monitoring ventricular rate or determining the presence of fibrillation on the basis of the probability density function (PDF) of an electrocardiographic signal. A system using the PDF technique statistically compares the location of points of a cardiac waveform with the expected locations of points of the normal waveform. When the waveform becomes irregular, as measured by its probability density function, an abnormal cardiac function is suggested. The latter technique is described in U.S. Pat. Nos. 4,184,493 and 4,202,340, both by Langer et al, the teachings which are incorporated herein by reference. In the Langer et al U.S. Pat. No. 4,202,340, probability density function is defined as “the fraction of time, on the average, that a given signal spends between two amplitude limits.” It has been noted that the probability density of an ECG changes markedly between ventricular fibrillation and normal cardiac rhythm. Accordingly, VF can be detected by providing a mechanism for generating a probability density function, or portion thereof, or approximately one or more points on the function. The entire probability density function need not always be developed; rather, it is sometimes sufficient to develop only particular values of the function at certain sampling points.
A more recent system, as disclosed in U.S. Pat. No. 4,475,551 of Langer et al and also incorporated herein by reference, utilizes both the PDF technique to determine the presence of an abnormal cardiac rhythm and a heart rate sensing circuit for distinguishing between ventricular fibrillation and high rate tachycardia (the latter being indicated by a heart rate above a predetermined minimum threshold), on the one hand, and normal sinus rhythm or a low rate tachycardia (indicated by a heart rate falling below a pre-determined minimum threshold), on the other hand.
Still further research in this area has resulted in the development of a heart rate detector system which accurately measures heart rate from a variety of different electrocardiogram (ECG) signal shapes. One such system is disclosed in U.S. Pat. No. 4,393,877 of Imran et al, the teachings which are also incorporated herein by reference.
An apparatus and method for treating tachyarrhythmias wherein the presence of a patient tachyarrhythmia is detected and a first anti-tachyarrhythmia therapy (anti-tachycardia pacing) is given at a first energy level has been proposed in U.S. Pat. No. 4,895,151 by Grevis et al, the teachings which are incorporated herein by reference. The hemodynamic condition of the patient is measured and a length of time to therapy switchover is continually derived during the application of the first anti-tachyarrhythmia therapy. The length of time to switchover is a function of the hemodynamic condition of the patient. When the time following detection of the patient tachyarrhythmia exceeds the length of time to switchover, a second anti-tachyarrhythmia therapy (a high energy shock) at a second energy level is provided. The average cardiac cycle length may be used as an indicator of the hemodynamic condition. Only a single hemodynamic parameter is utilized, at one time, in the Grevis et al apparatus, cardiac cycle length being the parameter illustrated.
An implantable cardiac stimulator that integrates the functions of bradycardia and anti-tachycardia pacing-type therapies, and cardioversion and defibrillation shock-type therapies, is disclosed in U.S. Pat. No. 4,830,006 of Haluska et al, the teachings which are incorporated herein by reference. The stimulator is programmable to provide a multiplicity of hierarchical detection algorithms and therapeutic modalities to detect and treat classes of ventricular tachycardia according to position within rate range classes into which the heart rate continuum is partitioned, and thus according to hemodynamic tolerance, with backup capabilities of defibrillation and bradycardia pacing at the higher and lower regions of the rate continuum outside the range of the ventricular tachycardia classes. Aggressiveness of the therapy is increased with elapsed time and increasing heart rate and detection criteria are relaxed with increasing heart rate and thus with increasing hemodynamic intolerance of the tachycardia.
A method for detecting and treating ventricular tachyarrhythmias of a patient's heart is disclosed in U.S. Pat. No. 5,002,052 of Haluska, the teachings which are incorporated herein by reference, which includes the steps of selectively dividing the heart rate continuum into regions including at least two classes of tachycardia, contiguous to each other and of progressively higher heart rate ranges, the lowest and highest of the tachycardia classes being bounded respectively by a sinus rate region and a fibrillation region of the continuum. The boundaries between the tachycardia classes and between the lowest and highest of those classes are selectively adjusted and the respective sinus rate and fibrillation regions to correspondingly adjust the rate ranges of the classes selectively detecting cardiac events anywhere within the continuum and distinguishing between normal and abnormal tachycardias. Treating a detected abnormal tachycardia with any of a multiplicity of therapy regimens of differing degrees of aggressiveness, toward terminating the detected tachycardia is proposed.
A process and apparatus for patient danger recognition and forecasting, particularly for the intensive medical care of the patient has been proposed in U.S. Pat. No. 4,197,854 to Kasa, the teachings which are incorporated herein by reference. The Kasa invention uses various variables to set up a danger function that represents the probability of occurrence of a danger condition, forms average values of the danger function throughout subsequent time periods that are shorter than the time required for a medical intervention. Formed average values with levels of increasing sequences of threshold values are compared providing an indication associated with the highest exceeded threshold value. The average values are used to set up a regression function which approximates the sequence thereof. A subsequent extrapolated value of the function is determined for the next time period that represents a forecast average value of the danger function. The extrapolated value is indicated, provided it is higher than a predetermined level. Preferably three threshold values are used in the comparing step, with magnitudes of 40, 60 and 80% of the danger function, respectively.
U.S. Pat. No. 4,770,177 of Schroeppel, the teachings which are incorporated herein by reference, discloses a pacer which paces a heart in accordance with the heart pacer rate needed to produce a required cardiac output while a person is exercising or undergoes emotional stress, in response to changes in venous blood vessel diameter. The pacer is adapted to be implanted in a human body and has a pulse generator and control circuitry, which may be realized by a microprocessor. A pacing lead adapted to be implanted in a heart has a tip electrode adapted to engage and supply pacing pulses to a right ventricle of a heart. A piezoelectric sensor determines changes in a diameter of a vein in the human body. Computing circuitry, including the control circuitry, relates the changes in venous blood vessel diameter with the required pacing rate needed to supply a desired cardiac output, and causes the pacer to pace the heart at the required rate when the heart is not naturally paced. The pacer of Schroeppel is not combined with any cardioverter and defibrillator.
Currently anti-tachycardia systems detect arrhythmias primarily by sensing rate and perform inadequately in the differentiation of hemodynamically stable from unstable rhythms. These devices, for example, may fire during a stable supraventricular tachycardia (SVT), inflicting pain and wasting energy. Damage to the heart may result.
A commonly used implantable anti-tachycardia device is the automatic implantable cardioverter and defibrillator which is commercially available. These devices continuously monitor myocardial electrical activity, detecting ventricular tachycardia (VT) and ventricular fibrillation (VF), and delivering a shock to the myocardium to terminate the arrhythmia. This cardioverter and defibrillator has been shown to reduce the mortality rate in patients with malignant arrhythmias with initial studies at Johns Hopkins Hospital and Stanford Medical Center demonstrating a 50 percent decrease in the anticipated total incidence of death, as reported by Mirowski et al, “Recent Clinical Experience with the Automatic Implantable Cardioverter-Defibrillator, Medical Instrumentation, Vol. 20, pages 285–291 (1986). Arrhythmias are detected by (1) a rate ® wave) sensor and (2) the probability density function (PDF) of an EKG signal which defines the fraction of time spent by the differentiated electrocardiogram between two amplitude limits located near zero potential. Presently, the functional window of the PDF is wide to permit the detection of both VT and VF, and therefore, this device functions essentially as a rate-only sensing system. As reported by Mirowski, “The Automatic Implantable Cardioverter-Defibrillator: An Overview”, JACC, Vol. 6, No. 2, pages 461–466, (August, 1985), when an arrhythmia fulfills either the rate or PDF criteria, the device delivers Schuder's truncated exponential pulse of 25 Joules some 17 seconds after the onset of the arrhythmia. The device can recycle as many as three times if the previous discharge is ineffective with the strength of the second, third and fourth pulses being increased to 30 Joules. After the fourth discharge, approximately 35 seconds of nonfibrillating rhythm are required to reset the device.
Closed loop intravenous drug delivery systems have been developed and are undergoing evaluation for the treatment of heart failure. Such systems may also be incorporated into an implantable device to permit the delivery of electrical therapy (pacing/cardioversion/defibrillation) as well as drug therapy, to correct a malfunctioning heart.
In addition to the standard automatic implantable cardioverter and defibrillator characterized by the above-noted dual detection algorithm, a variant of the device which features a sensing system that relies only on the analysis of heart rate is also available. This “rate-only” version of the known cardioverter and defibrillator preferred by some investigators, is more sensitive than the dual detection version unit and theoretically less likely to miss ventricular tachycardias with narrow QRS complexes. It is believed that the “rate-only” system, on the other hand, may be too sensitive, delivering cardioverting and defibrillating pulses too often or too soon, no hemodynamic parameter having been taken into consideration.
One drawback with many current systems is that they function primarily as a rate-only or single-hemodynamic-parameter driven systems and may fire for nonmalignant as well as malignant tachycardias. These firings are not benign; potentially endangering myocardium, wasting energy and inflicting pain on the conscious patient, all distinct shortcomings and disadvantages. Furthermore, these devices operate in a single mode; that is, such systems apply therapy, such as cardioverting and defibrillating pulses to the myocardium automatically, without the option or opportunity for confirmation or intervention by medical personnel.
External ST segment monitoring systems are also commercially available. These systems compare the normal or baseline ST segment of an ECG to that during normal exercise or activity to determine whether the change is significant and indicative of ischemia. Such monitoring systems are currently worn on the patient's waist or over the shoulders, and no active treatment is offered, since ischemia is only identified after the recording is complete, and the tape is scanned. It is possible that this information can be acquired in real time, such that appropriate drug therapy could be delivered to correct the ischemia.
The present inventor has developed practical systems and methods designed to in large measure overcome or ameliorate the deficiencies of the prior art. These patents, the teachings of each which are incorporated herein by reference, include U.S. Pat. Nos. 4,774,950; 4,899,751; 4,899,752; 4,967,748; 4,967,749; 4,984,572; 4,986,270; 5,014,698; 5,027,816; 5,054,485; 5,085,213; 5,119,813; 5,156,148; 5,163,429; 5,269,301; 5,330,505; and 5,417,713.
As but one example, a system for and method of treating a malfunctioning heart based on hemodynamics at a single site in a circulatory system was the subject of above referenced U.S. Pat. No. 4,774,950 by the present inventor and granted Oct. 4, 1988. Therein, the dynamics of mean arterial pressure (MAP) mean right atrial pressure (MRAP), mean right ventrical pressure (MRVP), mean left atrial pressure (MLAP), mean left ventrical pressure (MLVP) or mean central venous pressure (MCVP) were respectively proposed as the single-site or single-parameter basis for cardioversion and defibrillation, and both apparatus and method were disclosed. These aforementioned patents also disclose the incorporation of pharmacological therapies in further combination with cardioversion and defibrillation. As disclosed for exemplary purposes in U.S. Pat. No. 5,014,698 by the present inventor, the malfunction correcting circuits will produce malfunction correcting electrical output signals, which are delivered to the patient as required. Among these are signals which in turn control drug delivery devices, which may consist of a number of pumps or other drug delivery devices, such as gravity operated delivery systems supply medications to the patient in an effort to overcome or correct the malfunction. These output signals and/or drug(s) and/or the pumping assist are provided to effect termination of, or at least treat in an effective manner, singly or in combination stable SVT, unstable SVT, stable VT, unstable VT, stable atrial fibrillation, unstable atrial fibrillation, ventricular fibrillation, asystole, stable bradycardia, unstable bradycardia, ischemia, early infarction and both stable and unstable heart failure.
Although pharmacological and pacer therapy have ameliorated symptoms and improved the survival of patients with chronic heart failure (CHF) and other cardiovascular disorders, CHF remains a progressive disease causing incremental morbidity and early mortality. More recently, the results of the COMPANION trial demonstrated improved mortality and hospitalization in patients with heart failure who have an intraventricular conduction delay, through cardiac resynchronization achieved with atrial-synchronized biventricular pacing. Left bundle branch block in structurally normal hearts results in loss of synchrony of ventricular contraction and impairs both regional and global left ventricular systolic function. In hearts with good overall left ventricular systolic function this has very little clinical effect. But in patients with ischemic or idiopathic dilated cardiomyopathy it further impairs already poor systolic function and may have a major clinical impact. The prevalence of conduction delay in patients with heart failure has recently been estimated to approach 30%, and this has led to rapid development of biventricular pacing in an attempt to restore synchronous ventricular contraction and so improve left ventricular function. As an added benefit, based upon further recent studies, cardiac resynchronization seems to reduce the risk of clinical deterioration during follow up, with the combined risk of a major clinical event, defined as death or admission for worsening heart failure, being reduced by 40%. The number of patients requiring admission for heart failure also appear to involve a reduced number of total hospital days for management of heart failure.
Since the publication of the COMPANION results, there has been an exponential increase in biventricular cardioverter-defibrillator implants. These devices have a right atrial lead as well as a right and left ventricular lead. Two timing intervals, the atrioventricular (AV) delay and the RV to LV delay, can typically be manually programmed while measuring the patient's hemodynamic, either via echocardiography or via invasive hemodynamic monitoring or via transthoracic impedance. Exemplary of these devices and methods, and of varying relevance, are U.S. Pat. No. 5,584,868 by Salo et al; U.S. Pat. No. 5,836,987 by Baumann et al; U.S. Pat. No. 6,238,420 by Bakels et al; U.S. Pat. No. 6,567,700 to Turcott et al; U.S. Pat. No. 6,597,951 by Kramer et al; U.S. Pat. No. 6,606,516 by Levine; and U.S. published applications 2001/0031993 by Salo etal; 2002/0151938 by Corbucci; 2003/0018363 by Dinget al; 2003/0060851 by Kramer et al; 2003/0083700 by Hill; 2003/0100925 by Pape et al; 2003/0130702 by Kramer et al; 2003/0144703 by Yu et al; 2003/0199936 by Struble et al; and 2003/0204212 by Burnes et al, the teachings of each which are incorporated herein by reference.
As will be recognized from the substantial body of art incorporated herein above by reference, including numerous patents assigned to the present inventor and others, the electrical and mechanical arrangements necessary for the incorporation of technically advanced and flexible pacers and defibrillators is known in the art. However, successful implementation of the physical and electronic technologies for the ever broader effective clinical application has been somewhat more elusive. Among the various challenges faced are the varying underlying causes of a malfunctioning heart, the complexity of diagnosis and myriad of devices which may presently be required for appropriate application to a given root cause, the difficult set-up of these prior art devices for operation, and the risk of undesirable inappropriate functioning of the device.